Lung cancer is the leading cause of cancer related mortality in both men and women and remains a major health issue. More than 160,000 individuals will die from lung cancer in the coming year, more than breast, prostate and colon cancer combined. The majority of lung cancer cases is attributable to tobacco smoking and in some cases other environmental risk factors. Although the relative risk of developing lung cancer declines dramatically in smokers who quit, former smokers remain at risk for the disease. Several recent studies show that greater than 50% of newly diagnosed lung cancers occur in former smokers. Of the tumors detected in former smokers, nearly 50% occurred in patients who had quit for more than five years. It is estimated that there are approximately equal numbers of smokers and former smokers in the United States. Since smoking cessation is a major public health initiative, former smokers will increasingly account for a higher percentage of lung cancer cases. Thus, two high-risk population groups exist for lung cancer and improved disease management can be beneficial to both current and former smokers. Additionally the prognosis for lung cancer patients is very poor, as reflected by an overall, 5-year survival rate of only 14%. The poor prognosis for lung cancer patients is due, in part, to the historical lack of effective early detection measures. TUMOR SUPPRESSOR GENES (TSG) ON CHROMOSOME 9P:Chromosome 9p deletions and alterations occur early and often in lung cancer. The p16/CDKN2 locus, located on 9p, is suspected to be the major tumor suppressor gene inactivated in this tumor type. However, we have previously identified a region of homozygous deletion on the short arm of chromosome 9p. The minimal region of deletion detected was distinct from the p16/CDKN2 tumor suppressor gene locus, and lies approximately 2 cM proximal. We proposed that the region harbors a TSG important in lung tumorigenesis. We furthered our analysis by 30 non-small cell lung cancer and 12 small cell lung cancer cell lines by screening them with 55 markers to identify new regions of homozygous deletion on chromosome 9p. Three novel non-contiguous homozygously deleted regions were detected and ranged in size from 840 Kb to 7.4 Mb. One of these regions led to the identification of a gene identified as TUSC1. Multiplex PCR and Southern blot confirmed the homozygous deletion of TUSC1. Northern blot analysis of TUSC1 demonstrated two transcripts of approximately 2 and 1.5 kb that are likely generated by alternative polyadenylation signals. Both transcripts are expressed in several human tissues and share an open reading frame encoding a peptide of 209 amino acids. Analyzing lung cancer cell lines for RNA and protein expression demonstrated down regulation of TUSC1 in several cell lines suggesting TUSC1 may play a role in tumorigenesis. DNA sequencing of the TUSC1 gene open reading frame detected missense mutations in 7 of 41 cell lines examined and we are currently analyzing matched tumor and normal lung cancer samples to determine if somatic mutations occur in TUSC1. Studies using lung tumor cell lines stably transfected with TUSC1 show reduced proliferation both in vitro and in vivo. Taken together, these data suggest that chromosome 9p may contain other tumor suppressor genes important in lung tumorigenesis and that TUSC1 may be a candidate TSG. Current studies will examine how induction of TUSC1 expression will alter the phenotype of cells in culture. THE MAP3K8 GENE IN LUNG TUMORIGENESIS:The MAP3K8 gene is a MAP kinase kinase kinase expressed in a variety of cells and found to be oncogenic and constitutively activated when altered at the 3' end. However, mutation of the gene appears to be a rare event in humans, but altered MAP3K8 expression is associated with multiple tumor types.